Sympatho-adrenal responses to brief intermittent maximal exercise in man
The human sympatho-adrenal system (SAS) plays an iniportant role in the rapid and co-ordinated
cardio-respiratory, metabolic and hormonal adjustments necessary to facilitate the supply of
oxygen and fuels to exercising muscle.
AIM: The aim of this thesis was to examine the sympatho-adrenal responses to brief
intermittent maximal exercise and training with a view to contributing to our understanding of the
sympatho-adrenal response to this type of exercise.
METHODS: With University Research Ethics Committee approval all subjects completed a
laboratory based intermittent cycle test that consisted of ten maximal 6 s sprints against a
workload equivalent to 7.5 % of body mass with a 30 s recovery period between each sprint.
Blood samples were analysed for plasma catecholainines using HPLC with electrochemical
detection, catecholamine metabolites, mononuclear cell cAMP alongside blood acid-base balance,
electrolytes and metabolites.
RESULTS: The magnitude of the plasma noradrenaline (NA) and adrenaline (AD) but not
dopamine (DA) concentrations was determined by successive maximal cycle sprints. Significant
rela~onships were found between plasma NAand AD, blood acid-base status, metabolic and
Sprint trained (ST) atWetes demonstrated greater catechola.rD.ine responses to exercise compared
to untrained subjects (UT, P < 0.017) but no differences existed between endurance trained (ET)
and UT groups (NS). The mechanisms behind these findings were unrelated to the blood acidbase
status, plasma electrolyte or metabolites but were related to the higher pedal cadence (totalÂ·
pedal revolutions ST 120.1 Â± 4.0 VS. ET 112.4Â± 7.4 and UT 107.0 Â± 5.0 revs, P< 0.017).
The magnitude ofthe plasma catecholamine response to repeated cycle sprints was increased (NA
+34 %, AD +9 %, P < 0.05). There was no change in the exercise-induced elevations in the
catecholamine metabolites i.e. plasma nonnetanephrine and metanephrine concentrations (NS) as
a result of seven weeks of sprint training. Blood glucose and lactate were greater whilst plasma
potassium was lower following training (P < 0.05). Areduction in the isoproteronol-stimulated
cAMP content ofmononucl~ar cells with training was also evident (Rest; Pre-Train 1.8 Â± 1.6 and
Post-Train -0.4 Â± 1.5 pmol.rl and Post Exercise; Pre-Train 1.5 Â± 1.6 and Post Train -0.3 Â± 1.8
, P < 0.05).
Although significant changes in blood acid-base status were induced via consumption of sodium .
citrate no significant differences were found in the magnitude of the catecholamine response to a
controlled bout of high intensity cycle exercise between alkaline and control conditions
suggesting blood acid-base balance may not be important in influencing the magnitude of the
plasma catecholamine response to exercise.
CONCLUSIONS: The fmdings from the studies demonstrate that progressive increases in
plasma NA and AD but not DA concentrations occur in response to intermittent maximal cycle
exercise, and sprint training increases the magnitude of this response. Pedal cadence may explain .
some of the increases in sympatho-adrenal activity but changes in blood acid-base balance,
metabolites or electrolytes do not seem to playa role. Extraneuronal catecholamine metabolic
pathways are active following brief intermittent maximal exercise but are not modified with sprint
training. In contrast, mononuclear cell cAMP production is unaltered with acute exercise yet
appears to downregulate with sprint training suggesting a possible receptor-induced leucocyte
downregulation to isoproteronol stimulation.